1. Technical Field
The present disclosure relates to an adaptive filter for filtering an input signal, especially for filtering an input signal received over a mobile data network of a mobile communications system, and to a method for filtering such an input signal.
2. Description of the Related Art
EP 1 052 784 A1 describes an adaptive filtering for mobile communication systems and particularly for digital mobile phone systems. The method of EP 1 052 784 A1 determines filter coefficients of an adaptive filter in dependence on a detected error signal and a step size. Thereby, the step size for determining the filter coefficients is varied in dependence on an estimated frequency shift of a received signal from a nominal frequency value. The signal receiving method makes use of a Doppler frequency estimator to estimate the Doppler frequency from the difference between the expected frequency and the actual frequency.
The method of EP 1 052 784 A1 has the disadvantage that an additional Doppler frequency estimation is necessary, and hence means must be provided to measure the signal frequency and to estimate the Doppler frequency. The method of EP 1 052 784 A1 has the further disadvantage that only an indirect adaption of the step size for the adaptive filtering method with respect to effects based on a mobile phone speed is achieved.